With the increasing cheapness and reliability of microprocessors, it is natural to use them for the control of many complex systems which must be controlled with high precision and with rigorous standards of reliability. The microprocessor may be embedded within the overall system, or it may be -art of a stand-alone PC (personal computer) system such as is commonly available from a variety of sources. Among such systems are burner systems such as are used in boiler and heating systems and it is for such systems that the following disclosure is directed.
Once the change to microprocessor control has been implemented, it is relatively easy to add further functions of all types which improve the reliability, maintainability, efficiency, and flexibility of the system. By adding the appropriate sensors, it is also possible to monitor the operating status and by detecting slight changes in the operation, perhaps even perhaps even the approximate time when efficiency will fall below an acceptable level. This allows dealing with such problems during scheduled maintenance when the impact in terms of cost and convenience is least. It also allows maintenance to be deferred until actually cost effective, and then promptly performed.
Among the important considerations in the operation of a burner system is fuel efficiency. There are many different possible methods by which fuel efficiency may be sensed. For example, the efficiency may be determined more or less directly by sensing the change in heat energy contained by the fluid to which heat is transferred. Such a system requires measurement of flow rates and temperatures of the fluid to which heat is transferred, as well as the fuel flow rate. There is potential for errors in these measurements which can affect the accuracy with which the efficiency is determined. Since efficiency changes with firing rate and varies from one to another installation, simply calculating thermal efficiency for a given firing rate does not clearly indicate whether the burner is operating at the optimal efficiency for the operating state.
One can also analyze the constituents of the escaping flue gasses in measuring the fuel efficiency. However, each of the individual analyses is difficult, slow, and expensive. Accordingly, this approach does not lend itself to microprocessor implementation. An example of this approach is described in U.S. Pat. No. 4,994,959 (Ovenden, et al.), which teaches a burner control system where the fuel-air ratio is controlled on the basis of the amount of oxygen in the exhaust gasses. A stored table of preferred oxygen concentrations for different firing rates is used to control the air flow to the burner. The entries in the stored table are determined empirically. The purpose of this feature of the control system is to adjust the combustion process for maximum efficiency.
U.S. Pat. No. 4,373,663 (Hammer) discloses a burner control system which uses as one parameter on which the control algorithm is based the pressure of a working fluid such as water or steam.